1. Field of the Invention
The present invention relates to reflective antennas. More specifically, the present invention relates to an antenna capable of limiting minimum reflective beamwidth at higher frequencies while maximizing antenna aperture at lower frequencies.
2. Background of the Invention
Communications systems are increasingly reliant on satellites to transmit, receive, and redirect signals. Today""s satellites comprise a variety of materials and have a plurality of shapes and sizes. Satellite characteristics are typically based upon the requirements of a given application.
One type of antenna that is commonly used in space based applications is a parabolic antenna. Parabolic antennas are typically used to redirect a ground based signal either to another satellite or to another ground based receiving station. Parabolic antennas are typically used in applications where high gain is desired. However, these antennas can have other uses specifically suited for a given application.
One example of a parabolic antenna system is called Milstar. Milstar is an advanced military satellite communications system. The system comprises several satellites in geo-synchronous orbit. Each Milstar satellite serves as a switchboard in space by directing communications traffic from terminal to terminal anywhere on the Earth.
Several challenges exist for satellite systems such as Milstar. For example, maintaining the beamwidth of a signal from one ground station to another is a challenge currently facing system engineers. Typically, a beam containing information is transmitted to a space based satellite. A reflective antenna then sends the beam back to earth. Reflective antennas can have a many different shapes. Typically, however, a parabolic shape is used by those skilled in the art. With previous antennas, the beamwidth of a reflected signal decreases linearly as the frequency of a transmitted signal increases. This is because the beamwidth for a normal antenna is a function of several parameters, including the frequency of the signal and the diameter of the reflective antenna. A beamwidth that decreases with frequency is undesirable because a decreased beamwidth results in a smaller user area on the ground.
In order to avoid beamwidth decreases at higher frequencies, antennas must have smaller diameters as the frequency of a transmitted signal increases. This objective is tempered by the concurrent need to maintain large antenna apertures when transmitted signals are transmitted at lower frequencies. Many methods and apparatus have been employed to attempt to avoid beamwidth losses. The most common apparatus is an antenna with a horn feed. The horn beamwidth decreases as frequency increases, resulting in collection from a decreasing diameter of the reflective antenna. Alternatively, satellites have employed several reflective antennas with varying diameters. However, these methods are both costly and inefficient.
A continuing need exists for a reflective antenna that can preserve beamwidth at higher frequencies while maintaining antenna aperture at lower frequencies.
An object of the present invention is to provide an antenna formed by metallized mesh material with a mesh spacing that increases as the radius from the antenna center increases.
Still another object of the present invention is to use the increased mesh spacing to preserve a specified minimum bandwidth with increased frequency.
Yet another object of the present invention is to maintain antenna aperture at lower frequencies.
The present invention achieves the above and other objects by providing an antenna, comprising: a first set of conductors extending radially from a central point of the antenna; a second set of circular conductors; the first and second set of conductors being spaced about the central point of the antenna; and the spacing between adjacent ones of the circular conductors increasing with the distance from the central point.